Process fob the production of



Feb. 1l, '1936.` v Gpl.. CUNNINGHAM Re- 19,849

PROCESS FOR THE PRODUCTION OF CHLORINE DIOXIDE original Filed Fei. 2, 1954 Reisaued Feb. l1, 1936 UNITED STATES l Re.

PATENT ori-ICE PnocEss Fon 'rnE PaoDUc'rloN or cumming: Dioxins George Lewis Cunningham, Niagara Falls, N. Y., assigner to The Mathieson Alkali Works, Inc., New York, N.l Y., a corporation of Virginia 3Claima.

This invention relates to improvements inthe production of chlorine dioxide,'C10z. vMore particularly, the invention comprises a combination of steps forming a. cyclic process for the conversion of chlorine to chlorine dioxide. The process of the invention has several advantages. I-ligh eiliciencies in the conversion'of chlorine to chlorine dioxide 'can be attained. Chlorine, air and water are the only necessary raw materials, excepting fuel for heat and power. The process can be carried on to produce chlorine dioxide as the sole product without the production of waste products involving problems of loss and disposal.

The operation of the process of the invention l depends upon a reaction of magnesium chloride which distinguishes it from the chlorides of the alkaline earth metals and the alkali metals. This reaction is the thermal dissociation of magnesium chloride, in the presence of free oxygen, to form magnesium oxide, chlorine and hydrochloric acid. For example, at a temperatureapproximatlng 600-700 C., magnesium chloride dihydrate dissociates in the presence of free oxygen to form magnesium oxide, chlorine and hydrochloric acid, the reaction being illustrated by the following type equation:

'Ihis invention takes advantage of this reaction peculiar to magnesium chloride to` combine a number of steps in a unitary process. The relation of the dissociation step embodying thisreaction to the combination is illustrated, diagrammatically, in Figure l of the accompanying drawing, to which more detailed reference is made below.

'I'he process of the invention comprises, as j essential steps (l) separation of magnesium chloride and magnesium chlorate from a mixture of the same, (2) dissociation of magnesium chloride in the presence of free oxygen to form magnesium oxide, chlorine and hydrochloric acid, (3) generation` of a. gas mixture including chlorine and chlorine dioxide by reaction of magnesium chlo- 45 rate with hydrochloric acid (4) separation of chlorine from a gas mixture including `chlorine and chlorine dioxide by reacting the gas mixture with magnesium hydroxide and (5) chlorinating magnesium hydroxide, together with magnesium chloride and magnesium chlorate, to form a mixture of magnesium chlorater'and magnesium chloride. In the process of this invention, these steps are combined as follows: Magnesium chloride from the 1st step is supplied to the 2nd step and magnesium chlorate from the (ci. zza-zus) ist step is supplied to the 3rd step, iwdmchlcrie,l

acid from the 2nd step is supplied to the 3rd step, chlorine from the 2nd step` is supplied to the 5th step and magnesium hydroxide formed by hydration of magnesium oxide from the 2nd step is supplied tothe 4th step, the gas mixture including chlorine and chlorinedioxide from the 3rd step is supplied to the 4th step, magnesiumv hydroxide formed by'hydration of magnesium oxide from the 2nd step together with magnesium chloride and magnesium chlorate formed in the 4th step is supplied to the 5th step, and magnesium chlorate and magnesium chloride from the 5th step are supplied to the 1st step. Magnesium chloride formed in the 3rd step is with advantage returned to the 2nd step. Chlorine is supplied tc the 5th step and chlorine dioxide is recovered from the 4th step.- Again referring for the purpose of illustration to Figure l of the accompanying drawing, the ist step is the separation A", the 2nd step is the dissociation", the 3rd step is the generation the 4th step is the separation B and the 5th step is the chlorination.

The separation oi magnesium chlorate from magnesium chloride in the- 1st step of the combined operation may be carried out in any c onvenient manner. For example, this separation may be effected by fractional crystallization of the chloride from the chlorate, the latter being relatively more soluble. This separation is, how,- ever, with advantage eifected as described in my application nled February 9, v1934, Serial Number 710,530. As there described, the separation is eifected by extraction of magnesium chlorate from the mixture in acetone. For example, an aqueous solution containing magnesium chloride and magnesium chlorate, in a molecular ratio, MgCl2:Mg(C1O3) z, of about 5 l, from the chlorination is concentrated until the molecular ratio vof water present to magnesium chloride and magnesium chlorate, HzO:MgCla+Mg(ClQn) z, does not exceed about 6:1, and the resulting solid mixture is subjected to, countercurrent extraction with acetone at a temperature below about C. After evaporation of the acetone for reuse in the extraction, magnesium chlorate containing not more than 10% (by weight) of magnesium chloride can be recovered from the extract, the balance of the magnesium chloride being recovered as the-extraction residue.

In the second step of the combined operation, magnesium chloride is dissociated at a temperature approximating 600700 C. in the presence ot free oxygen, in the form of air for example.

The magnesium chloride is with advantage supplied to this operation containing at least as much water as corresponds to the dihydrate, MgCh.2HzO, but not much more. Reduction oi' the water content below this point tends to involve loss o! hydrochloric acid in the dissociation. The magnesium chloride separated in the first step, and magnesium chloride formed in the 3rd step with advantage added to the magnesium chloride from the lst step, may be dried to this extent by heating to a temperature upwards or 400' C. i'or example. Spray-drying indirect heat exchange with hot iurnace gases is advantageous in this connection. 'Ihe dissociation may be carried out in any convenient manner, for vexample by passing the dihydrate through a kiln, a rotary kiln for example, countercurrent to hot furnace gases, from the combustion or coal or'coke for example, containing -excess air sumcient for the dissociation reaction. The consequent admixture of carbon dioxide with the chlorine formed in the 2nd step assists the chlorination in the 5th step. Magnesium oxide is recovered as a solid residue and the chlorine and hydrochloric acid formed are evolvedy as gases. Hydrochloric acid is separated from this gas mixture by cooling the gas mixture and contacting it with water to recover the hydrochloric acid as concentrated aqeuous hydrochloric acid in the conventional manner. 'I'he remaining gas 'mixture, including the chlorine formed in the dissociation, is supplied to the 5th step.

'l'he generation of a `gas mixture including chlorine and chlorine dioxide in the 3rd step is elected by reacting the magnesium chlorate from the 1st step with hydrochloric acid from the 2nd step. TheA magnesium chlorate supplied to the* generation-should contain a minimum ot magnesium chloride and in no event should the molecular ration MgCh-:MgwlOah exceed 2:1.-

The magnesium chlorate is with advantage supplied to the generation as a concentrated solution in which the molecular ratio Mg(ClO:|) 22H20 approximates 1:4-8. The generation reaction is with advantage carried out in an aqueous solution subjected to aeration. The volume or air used should be such that the partial pressure oi chlorine dioxide in the resulting gas mixture does `not substantially exceed 25-30 mm. of mercury at standard conditions. By so diluting the chlorine dioxide produced, danger of explosion is minimised. The reaction eihciency is also improved. The following type equation illustrates the principal reaction occurring:

Ihe folhiwing type equation illustrates a side from. magnesium chloride and an amount oi' hydrochlorlc acid exceeding that stochiometrically required by about 16%, as much as 85%90% or i' more o! the chlorine supplied to the generation as magnesium chlorate is recovered as chlorine dioxide. The magnesium chloride solution produced in the generation reaction is with advantage supplied to the 2nd step with the mag- 70` nesium chloride from the lst step, as described above. Any free hydrochloric acid inv this solu-I tion is neutralized with part oi' the magnesium oxide from the 2nd step bei'ore this solution is returned to the 2nd step.

The separation in the 4th step of chlorine from step.

The following type equation will illustrate the Substantially all oi' the chlorine can thus be separated from the gas mixture without loss or chlorine dioxide. 'I'his mode of operation is described in an application led August 15, 1934, by James F. White, Serial No. 739,938. This separation of chlorine from the gas mixture including chlorine and chlorine-dioxide may'also be etlected as described in an application iiled August 15. 1934, by George P. Vincent, Serial No. 739,941. The hydration. oi' magnesium oxide from the 2nd step to form magnesium hydroxide -may be carried out in any convenient manner. For example this hydration may be eilected by boiling the magnesium oxide with water until hydration is complete or by heating the magnesium oxide with water or with steam at temperatures upwards o! 100 C. under superatmospheric pressure or with steam at temperatures upwards oi 100 C. under atmospheric pressure. The amount oi' magnesium hydroxide formed by hydration of' the magnesium oxide produced in the 2nd step, after allowance for magnesium oxide normally required to neutralize the magnesium chloride solution produced in the 3rd step, exceeds that necessary for reaction in the 4thstep with the chlorine of the gas mixture. includingchlorine and chlorine dioxide,` from the 3rd step. .All or part of this excess mag-v nesium hydroxide may be supplied to the 5th step through the-4th step or directly to the 5th step.

' In the 5th step, chlorination oi' the magnesium hydroxide from the 2nd step, partly chlorinated in the 4th step. yis completed. The following type equation will illustrate the reaction:

.This chlorination may be carried out in an aqueous solution or slurry in the conventional manner. lChlorine from the 2nd step and chlorine i'rom an extraneous source are supplied to this chlorination, the amount of chlorine re- 'quired to be supplied from an extraneous source corresponding to the amount of chlorine converted to chlorine dioxide, plus the losses? incurred in the combined operation. This chlorination advantageously is controlled so that the chlorinated liquor produced contains a` total oi' about 31% (by weight) of magnesium chloride and magnesium chlorate and so that the nal temperature attained in the chlorinationv approximates 60 C. After elimination of free chlorine and removal of sediment, in any conventional'manner, this magnesium chloride-magnesium chlorate solution is supplied to the lst The invention is further illustrated bythe accompanying drawing. in the form of: flow sheets, in which Figure 1 is a simplined diagram of the combination oi' steps forming the process of the invention and in which Figure 2 is a somewhat more detailed diagram representing a process embodying the invention. The same legends are usedtodesignate the samestepsinFigure land in Figure 2. Referring more particularly toFigure'2, the lseparatilm of hydrochloric acid from the 2nd step'isv the thegasmlxtureevolvedinthezndstepisthe separation C", the neutralization o! iree hydrochloric acid in the magnesium chloride solution from the 3rd-step with magnesium oxide from "neutralization andthe hydration of magnesium oxide from the 2nd stepior use in the 4th and 5th stepsis the hydration".

This invention comprises essentially .the combination of the' five steps above recited and illustrated in Figure 1 of the accompanying drawing. The steps forming this combination, severally, include other inventions, some inventions made by me and some inventions made by others associated with mein this connection.

I claim: v l

1. In the production ot chlorine dioxide, the process which comprises separating magnesium chlorate and magnesium chloride from amixture of the same, dissociating the separated magnesium chloride in the presence oi free oxygen to form rine and hydrochloric mixture including magnesium oxide, vchloacid, generating a. gas chlorine and chlorine dioxide from the magnesium chlorate from the first-mentioned separation by reacting said magnesium chlorate with hydrochloric acid from said dissociation, separating chlorine from lsaid gas mixture by reacting 'said gas mixture with magnesium hydroxide formed by hydration oi magsaid dissociation, chlorinathydroxide formed by hydration of magnesium. oxide from said dissociation together with magnesium chloride and magnesium chlorate formed in ,the second-mentioned sepa.- ration to form a mixture of magnesium chlorate and magnesium chloride and supplying that mixture to the mst-mentioned separation.v v

2. In the production o( chlorine dioxide, the which comprises separating magnesium chlorate and magnesium chloride from a mixture of thesame, dissociating the separated magneslum chloride in the presence of free oxygen to form magnesium oxide. chlorine and hydrochloric acid, generating' a gas mixture including chlorine and chlorine dioxide from the magnesium. chlorate from the first-mentioned separation by reacting said magnesium chlorate with hydrochloric acid from said dissociation, returning magnesium chloride formed in said generation to said dissociation, separating chlorine from said gas mixture by reacting said gas mixture` with magneslum hydroxide formed b v hydration oi magne alum oxide from said dissociation, chlorinating magnesium hydroxide formed by Ahydration oi. um oxide from said dissociation together with magnesium chloride and magnesium chlorate formed in the second-mentioned separation to form a mixture of magnesium chlorate and magnesium chloride and supplying that mixture to the mst-mentioned separation.

3. In lthe production of chlorine dioxide, the

process which comprises separating um chlorate and magnesium chloride from a. mixture o! the same, dissociating the separated magneslum chloride in the presence oi free oxygen to form magnesium oxide, chlorine and hydrochloric acid, generating a gas mixture including chlorine and chlorine dioxide from the magnesium chlorate from. the mst-mentioned separation by reacting said magnesium chlorate with hydrochloric acid from said dissociatio returning magnesium chloride formed in said generation to said dissociation alter neutralizing unreacted hydrochloric acid with magnesium oxide from said dissociation. hydrating the remaining magnesium oxide irom said dissociation. separating chlorine from said gas mixture by reacting said gas mixture 4withmagnesium hydroxide from said hydration, chlorinating magnesium iwdroxide from said hydration together with manesiurnzchloride and magnesium chlorate formed in the second-mentioned separation to form a mixture of magnesium chlorate and magnesium chloride and supplying that'mixture to the mst-mentioned separation.

GEORGE LEWIS CUNNINGHAM. 

